Allow organizations to add their own Spamhaus key for mail reputation checks #188

Summary

Let organizations add their own Spamhaus Data Query Service (DQS) key so SendLit can run mail reputation (blocklist) checks using the org's own credential.

Requirements

• Org-admin management: org admins can add, replace, test, and remove the Spamhaus DQS key.
• Secure storage: key is stored server-side as an org-isolated secret; masked in the UI after saving; never written to logs or exposed to the client.
• Usage: teams in the org use the org credential for supported blocklist checks on their sending IPs/domains.
• Clear results: distinguish listed, clean, error (e.g. invalid key, quota, network), and unconfigured.
• No fallback: if no key is configured, report unconfigured — no free or shared SendLit key fallback.

Notes

• Using Spamhaus in a hosted/commercial product requires an appropriate Spamhaus commercial subscription; the free service is limited to non-commercial use (fair-use terms). Each org is responsible for its own subscription.
• Out of scope: spam-content scanning; this does not guarantee inbox placement.